Reactance tube system



March 20, 1945. w VAN ROBERTS 2,371,651

REACTANCE TUBE SYS TEM Filed Jan. 28, 1943 5 Slieets-Sheet 1 PFO To OSC/L L970? l6 CONTROL VOL 76 lNVE/VTOP. Wallr ar:Z.R erZIY 5y W Ar ruP/VEY Mrch 20, 1945. V N a ROBERTS 2,371,651

REACTANCE TUBE SYSTEM Filed Jan. 28, 1943 3 Sheets-Sheet 2 March w. VAN B. ROBERTS ,6

REACTANCE TUBE SYSTEM Filed Jan. 28, 1945 3 Sheets-Sheet 3 vkFo lA/VE/VTOk: VEer Van/417.303 eriii' ,mean frequency of Patented Mar. 20, 1945 2.871.681 nmcrsacn roan srsrm Walter van 3.

\ tion of Delaware Roberts, Princeton, N. to Radio Corporation of America,

8., minor a corpora- Application January as, ms, Serial 'No. 474.51:

15 Claims.

This application relates to a reactance tube circuit substantially free of resistance component. which rcactance may be used, for example, to control the frequency of an oscillator or oscillation circuit over a wide range. In one modification an efiective negative inductance is provided while in another modification an effective negative capacity is provided, both free of resistive components. In a third modification both the above effects are provided simultaneously by the use of a complementary circuit which, in some aspects. resembles a push-pull circuit, and are used to control the frequency of an oscillation generator or oscillation circuit. The eilectivc reactances provided in all of the modifications may be used in the phase shifting circuit of a reactance tube modulator or modulators associated with an oscillation circuit.

The oscillations generated by the oscillator or. flowing in the circuit may be controlled as to phase or frequency or modified forms of either or both, or may be controlled in accordance with potentials which vary with slow changes in the enerated oscillations or wave energy combined therewith, in the manner commonly referred to as automatic frequency control.

made to the attached drawings, wherein Figure 1 illustrates somewhat schematically an oscillation circuit, a negative capacity substantiaily free of resistance, including a tube coupled to the oscillation circuit and a reactance tube in circuit with the first tube and with the oscillation circuit for controlling the tuning of the said oscillation circuit.

Figure 2 illustrates a modification of the ar-' rangement of Figure l. The modification of Figure 2 includes with the negative capacity a negative inductance, the capacity and inductance being associated with a reactance tube, which. in turn, is connected with a timed circuit to control the tuning thereof.

Figure 3 illustrates a modification oi the arrangement of Figure 2. In Figure 3 independent bias circuits are provided for the tubes providing the negative reactance effects and the reactance tubes, there being a reactance tube for each negative reactance, whereas in Figure 2 a single reactance tube is used.

Figures 3a and 3b are modifications of the arrangement of Figure 3. v

Figure 4 is a simplified diagram used in describing the operation of the arrangement of Figure 3.

In describing my invention reference will be In Figure 1, Ill represents a tank circuit, such as. for example, the tuned circuit of an ocillator or of a high frequency relaying tube. The tank circuit includes a tuning condenser C and is connected at its high potential end by a small condenser CI to the control grid GI of a first tube ll and also to the anode of a second tube It. The cathodes of both tubes are connected to the low potential end of the tank circuit In. The grid GI of tube It is connected to the low potential point by condenser 02. The anode of tube It is coupled by inductance L and resistance r and coupling condenser 20 to the grid G2 of tube IS. The cathodes of tubes l4 and it are coupled by biasing circuits to ground. Control voltages may be supplied to Gi or G2 or both by way of grid leak resistances 22 and 24. As described later a reactive eflect is developed in tube It and this reactive eifect being in the circuit ill by virtue of 20 the coupling of the output electrodes of tube It across l0 determines thereby controls the frequency of the oscillations therein.

If E is the R. M. S. voltage across the circuit so it, the grid GI of the first tube receives EZ1Z2 i It 'z 1+z2 Z1 8 where Zl is theimpedance of Cl and Z2 is the 80 impedance of C2 and conductance 6 of resistance 22 in parallel. This grid voltage may be written 'rtci c+joC2+joC1 35 The plate current of the first tube is is oi times the grid voltage and flows through impedance r+iwL so that the grid voltage of the second tube is r-I-Z'mL t+ o c2+c1 It now we choose /--.+L "CH-0'2 45 the current drawn b thesecond tube I 6 from the tank becomes simply 201- C2 sothat the tube I 6 acts like a negative capacity so of value the tuning thereof and In practice, the second tube I8 can put only a .limited amount of alternating current so that the maximum volt-amperes of wattless current it of E and the maximum current output of the second tube I5. But the wattless volt-amperes in the oscillator tank per se is EwC' so that the greatest effect on the oscillation frequency will occur when E is chosen small (to permit the tube I4 acting as a large negative capacity while not drawing more than allowable current from the second tube I6) while '0 is chosen to just equal this negative capacity. In this case, the oscillacan supply to the tank circuit IIIis the product analysis thereof given hereinbefore, it is seen that i the tube I4 acts like a pure reactance, while if r is small 6 is also small and in practice is very small so that the conductance across the tank I0 due to the circuit CI C2 6 is very small.

The chief feature is that the voltage on the grid G2 of the tube I8 is in exact quadrature with the tank III voltage at all frequencies. A s'ubsidiary feature is that on account of the extra tub I4, and the fact that its grid voltage is nearly in phase with the tank voltage,- there is very little conductance introduced across the tank circuit ID by the grid excitation circuit CI C2 6.

The control voltage may be applied to the grids of both tubes as shown, or in any proportion. Preferably it will be so proportioned that on the negative swing both tubes cut off at the same time, while on the positive swing both tubes attain maximum transconductance at the same time.

With the present circuit, the frequency can be swung from the natural frequency of the tank per se, up to a very high frequency, as the negative capacity of the tube system balances out the actual capacity across the tank coil.

In the modification of Figure 2 is provided either negative capacity or negative inductive susceptance according to the ratio of the control voltages on the tubes I4 and I4. The tube I4 has its control grid GI connected between condenser CI, C2. The tube l4 has its control grid GI connected between condensers CI and C2 so that both grids are excited by voltages of substantially the same phase from the high potential end of tank circuit I0. The modulating or controlling potentials are applied differentially by means of a transformer 30 between the control grids GI and G'I. The anode of tube I4 is coupled by an inductive reactance designated I by +2! and a coupling condenser I! to the control grid G2 of the reactance tube I6; while the anode of tube I4 is coupled by a capacitive reactancedesigned ---KY and a coupling condenser I8 to the same control grid G2 of tube I6.

One phase shifter produces output voltage 01 c 1+ c2 The other phase shifter produces output voltage These two voltages are combined through the small coupling condensers I1 and I8 on the grid G2 of the reactance tube I6, and the values of gl and 2 are differentially modulated, as by push-pull grid control voltage input.

Analysis shows that the oscillation frequency can be reduced by the action of the lower tube to about the same extent as it can be increased by the upper tube. v

The amount of frequency swing obtainable is determined by the ratio of wattless volt-amperes available from the reactance tube. to the geometric mean of the volt-amperes flowing in the physical coil and in the condenser of circuit In at the limit of the swing. This can be made large by operating the tank at low voltage and using a tank of large L/C ratio. The LG product, of course, determines the mean frequency, 1. e., the frequency that occurs whengI=g2 so that the reactance tube is not supplying any current.

The arrangement of Figure 3 makes use of the principle described hereinbefore. In Figure 3, however, I make use of two reactance tubes I6 and I6' having their control grids G2 and G2 coupled by coupling condensers to the anodes of the tubes I I and I I and to the secondary winding of a transformer T2 in push-pull relation. The coupling between the control grid G2 and the anode of tube Il includes an inductance L and a resistance rl, while that between. the grid G2 and the anode of tube I4 includes a resistance r2 and condenser K.

The grids GI and GI' are connected to the secondary winding of a second transformer TI.

The primary windings of the transformer TI and T2 are in parallel and supplied with the desired modulating potentials from source 30.

Transformers TI, T2, and sources 32 and 36 provide one way to supply independently adjustable bias and difierential modulation to the reactance tubes I6 and I6 and to the tubes It and I4. I

In each system, if there is any appreciable phase shift between grid voltage on GI (or GI) and 13, due to undesired efiectiveconductance located as at 61 (or 62) this shift may be compensated by introduction of sufficient resistance 11 (or m) with the result that the voltage on G2 lags E by exactly while that on G2 leads E by 90 over a wide range of applied frequencies.

It is necessary for this compensation that voltage for one grid, say GI, be tapped from an inductive voltage divider LI, L2 (here shown as the inductive branch of the oscillation tank) while the voltage for the other grid (GI) be tapped from a capacitive divider CI, C2 (here acting also as capacitive branch of the oscillator tank). This can be proved as follows and in the explanation reference will be made to Figure 4.

Voltage at G (admittance of elements Z1, Z2, and 6 con- Z l sidered as connected in parallel) Call this admittance 1!.

Voltage at the ratio 22/ is real.

n the other hand if as is the case in the lower phase shifting system, then impedances ZI and Z2 must be pure inductances' so that the admittance of 62 in parallel with ZI and Z2 will be of the form (L1+L'2 in which case the ratio 23/11 will obviously be real and constant if T: L1; L2

It should be emphasized that other networks are possible for deriving from E an input voltage for GI (or GI) and that for any such network the desired 90 phase shift at the grid of G2 (or G2) may be obtained by suitable construction of the load circuit of the stage connecting GI to G2 (or GI to G2). Furthermore, for many applications it is not important that the phase shift be exactly 90 over a wide range of frequencies, and it is within the scope of the present invention to deliberately employ networks .which give a phase shift that departs from 90 somewhat, as a function of frequency, so as to introduce some regenerative component at frequencies where the amplitude of oscillation tends to fall off, or to introduce degeneration at frequencies of excess oscillation amplitude, or both.

In order to obtain the greatest possible frequency swing, the various circuit elements and voltages should be adjusted so that on one peak of the modulating voltage tube It is delivering the maximum volt-amperes of which it is capable, while I8 is delivering none. The oscillation frequency will then be a maximum. On the other peak of the modulation, tube It is cut oil and tube I8 delivers maximum output and the frequency is a minimum. Without modulation input, the outputs of tubes I6 and I6 may be zero individually and in any case will be equal and of opposite phase so that the frequency of oscillation will be simply that of the tank itself.

While the system will operate with modulating voltage applied to either or both of the tubes in each system, and with a range of bias voltages, it is recommended that for any given installation a cut-and-try" determination of the best bias and modulation input be employed.

For any given desired value of E, the radio frequency voltage applied to GI and the product of tube transconductance and impedance in its plate circuit should be chosen to cause maximum output from tube It at the peak of modulation voltage, if maximum frequency increase is to be obtained. The same remarks apply to tube I8 for greatest decrease of frequency.

The tube 26 is a generator of the regenerative type and generates the voltage flowing in the tuned circuit Ill.

The modification in Figure 3a is in many respects similar to the arrangement of Figure 3. In Figure 3a, however, a single reactance tube l6 is required and is used somewhat as in Figure 2. Modulation is applied to the grids GI and GI' as in Figure 3 and may also be'applied by way of switch 8 and transformer T4 to the desired extent to the grid G2 of tube II. If desired the modulation need not be applied to the grid G2 in which case switch 8 is opened.

In the modification of Figure 3b the anodes of tubes I4 and II are coupled by an inductance L and a coupling'condenser I? to the grid G2 of tube It. Modulation is applied to tubes II and It only with bias supplied by a variable source 28. Radiofrequency voltage from tank III is supplied from a capacity divider CI 02 to the grid GI and an equal but conjugate phase radio voltage is supplied by inductance L5 coupled to inductance L2 to the grid GI of tube II. fIhus equal and substantially opposed radio frequency voltages are supplied to the grids GI and GI. The total current through L has therefore no component in quadrature with the tank voltage E so long-as the transconductances of tubes I4 and H are equal, as is the case in the absence of modulation.

The term co-linear phase is believed to aptly designate voltages which may be either in phase or in phase opposition.

claim:

1. In a system of the nature described, a tank circuit wherein wave energy the wave length of which is to be controlled appears, an electron discharge phase shifter tube having electrodes including an anode, a cathode, and a control grid, a reactance tube having electrodes includ ing an anode, a cathode, and a control grid, a coupling between the cathodes of the tubes and the tank circuit, a connection for impressing voltage from the tank circuit in substantially co-linear phase, with respect to the phase of the tank circuit voltage, on the control grid of said phase shifter tube, an output load of approximately pure reactance connected with the anode of said phase shifter tube, connections between said load and the control grid of the reactance tube for exciting said control grid by the voltage developed across said lead of substantially pure reactance, means for establishing the desired phase relation between the voltage across said load and the voltage on the control grid of the phase shifter tube including a resistance connected to the anode of said phase shifter tube of a value sufficient to compensate undesired effective conductance in connections to the control grid of the phase shifter tube, and a coupling between the anode and cathode of the reactance tube and the tank circuit.

' 2. A system as recited in claim 1 wherein said substantially pure reactance is inductive in character and said phase shifter tube simulates a negative capacity.

3. A system as recited in claim 1 wherein said substantially pure reactance is capacitive in character and wherein said phase shifter tube simulates a negative inductance.

4. In a system of the nature described, a tuned circuit wherein wave energy the wave length of which is to be controlled appears, an electron discharge phase shifter tube having electrodes including an anode, a cathode, and a control grid, a reactance tube having electrodes including an anode, a cathode, and a control grid, connections for impressing voltage from the tuned circuit in substantially co-linear phase on the control grid of said phase shifter tube, an output load of approximately pure reactance connected with the anode of said phase shifter tube, connections between said load and the control grid of the reactance tube for exciting said control grid by the voltage developed across said load of substantially pure reactance, a resistance in the anode circuit of said first tube to compensate or oflset departures of the impressed voltages from co-linearity over a wide range of frequencies, and a coupling between the anode and cathode of the reactance tube and the tank circuit.

5. A system as recited in claim wherein said substantially pure reactance is inductive in character and said phase shifter tube simulates a negative capacity.

6. A system as recited in claim 4 wherein said substantially pure reactance is capacitive in character and said phase shifter tube simulates a negative inductance.

'7. In a system of the nature described, a tank circuit wherein wave energy the wave length of which is to be controlled appears, a pair of electron discharge phase shiftertubes each having electrodes including an anode, a cathode, and a control grid, a pair of reactance tubes each having electrodes including an anode, a cathode, and a control grid, connections for impressing voltages from the tank circuit insubstantially co-linear phase on the control grids of saidphase shifter tubes, an output load of approximately pure reactance connected with the anode of each of said phase shifter tubes, said reactances being of op-. posite sign, connections between said loads and the control grids of the reactance tubes for exciting said control grids by the voltage developed across said loads of substantially pure reactance, and a coupling between the anodes and cathodes of the reactance tubes and the tank circuit.

8. A system as recited in claim 7 wherein one of said substantially pure reactances is capacitive in character, the other is inductive in character and one cf-said phase shifter tubes simuload of substantially pure reactance connected with the anode of one of said phase shifter tubes, 'a load of substantially pure reactance of a sign opposite to the sign of said first reactance connected to the anode of the other of said phase shifter tubes. a coupling between said respective loads and the input electrodes of a different one of the reactance tubes, and means for applying control potentials differentially to electrodes of said two phase shifter tubes and to electrodes of said reactance tubes.

ll. In a system of the nature described, a tank circuit wherein wave energy the wave length of which is to be controlled flows, a pair of tubes each having a control grid, a cathode, and an anode, a reactance tube having input and having output electrodes coupled across said tank circuit, connections for applying voltage from the tank'circuit substantially co-linearly on the control grids of said pair of tubes, a load of substantially pure reactance connected with the anode of one tube of said pair of tubes, a load of substantially pure reactance of a sign opposite to the sign of said first reactance connected to the anode of the other tube of said pair of tubes, a coupling between said loads'and the input electrodes 'of the reactance tube, and means for applying control potentials differentially to the input electrodes of at least two of said tubes.

12. In a system of the nature described, a tank circuit wherein wave energy the wave length of which is to be controlled appears, an electron discharge phase shifter tube having electrodes including an anode, a cathode and a control grid, a reactance tube having electrodes including an anode, a cathode and a control grid, a capacity potential divider including at least two capacities in shunt to said tank circuit, con- 0 nections coupling the control grid and cathode lates a negative inductance while the other of said phase shifter tubes simulates a negative capacity.

9. In a system of the nature described, a tank circuit wherein wave energy the wave length of whichis to be controlled flows, a pair of phase shifter tubes each having electrodes including a control grid, a cathode, and an anode, a reactance tube having input electrodes and having output electrodes coupled to said tank circuit, connections for applying voltage from the tank circuit substantially co-linearly on the control grids of said pair of phase shifter tubes, a load of substantially pure reactance connected with the anode of one of said phase shlfter'tubes, a load of substantially pure reactance of a sign opposite to the sign of said first reactance connected to the anode of the other of said phase shifter tubes, 9, coupling between said loads and the input electrodes of the reactance tube, and

means for applying control potentials differentially to electrodes of said t o phase shifter tubes. v

10. In a system of the nature described, a tank circuit-wherein wave energy the wave length-of which is to be controlled fiows, a pair of phase shifter tubes each having electrodes including a control grid, a cathode, and an anode, a pair of reactance tubes each having input electrodes and each having output electrodes coupled to said tank circuit, connections for applying voltage from the tank circuit substantially co-linearly on the control grids of said phase shifter tubes, a

of said phase shifter tube across at least one of said capacities for impressing voltage from the tank circuit in substantially co-linear phase, with respect to the phase of the tank circuit voltage, on the control grid of the phase shifter tube, an output load of approximately pure reactance connected with the anode of said phase shifter tube, connections between said load and the control grid of the reactance tube for exciting said control grid by the voltage developed across said load of substantially pure reactance, a coupling between the cathode of said reactance tube and said tank circuit, and a coupling between the anode of said reactance tube and said said tank circuit.

13. In a system of the nature described, a tan. circuit wherein wave energy the wave length of which is to be controlled appears, an electron discharge phase shifter tube having electrodes including an anode, a cathode, and a control grid, a reactance tube having electrodes including an anode, a cathode, and a control grid, a coupling between the cathode of the reactance tube and put load of approximately pure reactance 0011- nected with the anode of said phase shifter tube, connections between said load and the control grid of the reactance tube for exciting said control grid by the voltage developed across said load of substantially pure reactance, and a coupling between the anode and cathode of the reactance tube and the tank circuit.

14. An arrangement as recited in claim 1,

wherein said tank circuit has a capacitive branch 10 and an inductive branch and wherein said connection for impressing voltage from the tank control grid of the phase shifter tube is to the capacitive b'ranch of the tank eircui WALTER van 3. ROBERTS. 

